1. Field of the Invention
The present invention relates to a method of setting welding parameters in an integrated control system in which a robot controller for controlling an operation of a robot, and a welding controller including a timer and a contactor for controlling the welding current and the welding time (hereinafter, such a controller is referred to as a welding timer) are integrated with each other, and which, through a teaching pendant, centrally manages welding parameters and other processes such as teaching of the robot, reading and writing of input and output data, and monitoring.
2. Description of the Related Art
A robot controller for a resistance spot welder and a welding timer are conventionally integrated with each other in a control system. For example, a control method disclosed in JP-A 7-144283 and that disclosed in JP-A 10-58157 are known as the control system.
In the former method, a servomotor as a driving source is used in a pressure actuator, which is used for an electrode of a spot welder. The pressure actuator starts a pressurizing operation in response to a weld start signal supplied from a robot controller. Then, the robot controller controls a robot to move in response to a weld completion signal supplied form a controller for the pressure actuator.
During the welding time from an electrode pressurization to an electrode opening in the spot welder, a force of pressurizing the electrode is synchronized with the welding current. The force of pressurizing the electrode is controlled by the controller for the pressured actuator. The welding current is controlled by a welding timer for controlling a switch of a welding source.
In the latter method, a spot welding timer and a pressurizing force controller are connected to each other via a system bus. The spot welding timer and the pressurizing force controller are synchronizingly controlled by a robot controller. In accordance with stored welding data, the robot controller synchronizingly changes in plural steps both the pressurizing force and the welding current.
In teaching of welding sequence data by the above-described control method, a control method is known as shown in FIGS. 1 and 2. Both a welding timer and a robot controller are connected to each other by a field bus. The welding sequence data are set into the welding timer via the field bus by a teaching apparatus which is connected to the robot controller.
In this case, the following system is usually employed (see JP-A 2001-58275). A setting screen depends on a program of a robot side. For example, setting items such as “squeeze (cycle)”, “slope (cycle)”, “energization 1 (cycle)”, and “current 1 (amp)”, and the sequence of “1”, “2”, “3”, “n” are set to a fixed format when the program is prepared.
A welding controller transmits values of the welding parameters “30”, “3”, “10”, “8000”. Each time when the welding parameters are added or changed due to modification of the specification of the welding controller, both the editing screen (item names and arrangement sequence) for the welding parameters of the robot side and the screen format must be changed. As a result, software must inevitably be modified so that the cost is increased.
Conventionally, a robot controller and a welding timer usually communicate with each other via an I/O unit or an interface based on serial communication as shown in, for example, FIG. 3. The robot controller operates a resistance spot welder and controls pressurization of electrode tips of the welder. The welding timer performs a welding control-such as a welding time and a welding current.
In the configuration shown in FIG. 3, when welding is to be started, the robot controller gives a weld command to the welding time at the same time the robot controller pressurizes and drives the electrode tips at a predetermined pressurizing force set in the robot controller; The welding timer, which receives the weld command from the robot controller, performs a welding control; and, after welding is ended, a welding ending signal is issued to the robot controller.
In the robot controller, a pressurization control method is employed in which the electrode pressurizing force is maintained to a constant level during a period from the start of the pressurization to a timing when the welding ending signal is received.
In this case, such a resistance spot welder pressurizes and drives the electrode tips while converting rotational motion into linear motion under an electronic control by a microcomputer, by a mechanical drive unit such as a screw nut and a ball screw, a reduction gear, a rack and a pinion, or a cam. According to the configuration, a torque for a pressurizing force required for welding is generated between the electrode tips to squeeze welded articles. Then, a predetermined current is supplied to the electrode tips via a welding transformer connected to the welder, thereby performing spot welding. Such a welder is operated by a robot controller to be used in a process of assembling the body of an automobile, etc. Usually, spot welding guns of the C type or the X type are used.
In the above paragraph, although it is not usual to variably pressurize the electrode tips during a welding process, variable pressurization during a welding process can be performed by using a time counter incorporated in the robot controller. For example, a method may be contemplated in which an arbitrary electrode pressurizing force and an arbitrary pressurizing force changing timing are set in the robot controller. When welding is to be started, the robot controller pressurizes and drives the electrode tips and gives a weld command to the welding timer, and the welding timer performs a welding control. After a predetermined time is counted by the time counter, the robot controller changes the pressurizing force of the electrode tips to a predetermined value.
In this method, the electrode pressurizing force during a welding process is managed by the robot controller, and therefore it is impossible to variably pressurize the electrode tips in synchronization with the welding timer.
In the related art, the robot controller conventionally maintains a waiting state in the system until the welding control is ended by the welding timer. However, variable pressurization during a welding process can be performed by using a time counter incorporated in the robot controller.
For example, an arbitrary electrode pressurizing force and an arbitrary pressurizing force changing timing are set in the robot controller. When welding is to be started, the robot controller pressurizes and drives the electrode tips and gives a weld command to the welding timer, and the welding timer performs a welding control in accordance with a preset welding time. By contrast, a method may be contemplated in which, after a predetermined time is counted by the time counter, the robot controller changes the pressurizing force of the electrode tips to a predetermined value.
In this method, the pressurizing force changing timing during a welding process is managed by the robot controller, and the welding time is managed by the welding timer. Therefore, the pressurization control performed by the robot controller cannot be synchronized with the welding control performed by the welding timer, with the result that it is impossible to perform a variable pressurization control on the electrode pressurizing force.